Acute Labyrinthitis - Clinical Features, Investigations, and Treatment Protocol

Definition and Classification

1. Serous labyrinthitis - inflammation without pus formation; bacterial toxins/mediators enter via the oval window, round window, or labyrinthine fistula without bacterial invasion of the labyrinth itself
2. Suppurative (otogenic or meningitic) labyrinthitis - actual bacterial infection within the labyrinth
3. Viral labyrinthitis - presumed viral etiology, no bacterial source identifiable

• Shambaugh Surgery of the Ear, pp. 3938-3941
• K.J. Lee's Essential Otolaryngology, pp. 867-927
• Scott-Brown's Otorhinolaryngology Vol. 2, pp. 3901-3925

Etiology

Bacterial Causes

• Serous labyrinthitis: most commonly complicates acute otitis media (AOM). Bacterial toxins (especially streptococcal) increase round window membrane permeability, allowing entry without direct bacterial invasion. Common pathogens: Streptococcus pneumoniae, H. influenzae, M. catarrhalis
• Suppurative (otogenic): bacteria enter via labyrinthine fistula (most commonly from cholesteatoma), surgical defect, or congenital anomaly. Most commonly associated with cholesteatoma in the modern era
• Suppurative (meningitic): bacteria enter via cochlear aqueduct or IAC from the subarachnoid space. Important route in children with cochlear implants and congenital inner ear malformations

Viral Causes

• Presumed viral etiology when acute-onset vertigo + SNHL occur without identifiable otologic or meningitic cause
• Implicated viruses: HSV type 1 (reactivation model), CMV, mumps, measles, rubella, varicella-zoster (Ramsay Hunt)
• Definitive viral isolation from perilymph is rarely achievable; identification remains elusive in most cases
• Cummings Otolaryngology, pp. 1836-1843

Clinical Features

Symptoms

• Direction-fixed, horizontal nystagmus beating away from the affected ear (inhibitory type)
• Nystagmus beating toward the affected ear is an ominous "irritative" sign indicating acute inner ear injury - Scott-Brown's Vol. 2, p. 3910-3911

• Acute phase: 48-72 hours of severe vertigo
• Subacute phase: dysequilibrium and unsteadiness for 4-6 weeks
• Chronic recovery/compensation: may persist several months

Investigations

Bedside Assessment

• Otoscopy - middle ear effusion, TM perforation, cholesteatoma (purulent AOM or COM with cholesteatoma suggests suppurative type)
• Head impulse test (HIT) - positive (catch-up saccade) in peripheral vestibulopathy; helps confirm peripheral origin
• HINTS exam (Head Impulse - Nystagmus - Test of Skew) - to rule out central cause (normal HIT + direction-changing nystagmus + skew deviation = central; always exclude posterior circulation stroke)
• Dix-Hallpike - to exclude BPPV

Audiological

• Pure tone audiogram - SNHL, often in high frequencies; may have additional conductive component if middle ear disease present
• Speech audiometry - assess word recognition score
• Tympanometry - assess middle ear status
• DPOAE/TEOAE - may show outer hair cell loss in basal turn
• Histopathology (if available): loss of outer hair cells primarily in basal turn, with significant incidence of endolymphatic hydrops - K.J. Lee, p. 908

Vestibular Testing (when necessary)

• Caloric testing / VNG/ENG - canal paresis on affected side
• VEMP (cervical/ocular) - saccular/utricular assessment
• Video head impulse test (vHIT) - quantifies VOR gain deficits per canal

Microbiology

• Culture of middle ear effusion when present (to guide antibiotic therapy)
• Blood cultures if febrile/systemically unwell
• CSF analysis if meningitis is suspected

Imaging

• MRI with gadolinium contrast (T1 post-contrast): prominent enhancement of the cochlea and vestibule - the gold standard for diagnosing acute labyrinthitis radiologically. Enhancement reflects blood-labyrinth barrier disruption due to capillary endothelial damage

• CT temporal bones - not helpful in diagnosis of labyrinthitis itself, but delineates underlying anatomical abnormalities (cholesteatoma fistula, cochlear malformation, ossification in chronic cases)
• MRI/CT is not indicated in straightforward serous or viral labyrinthitis without other suspected complications - K.J. Lee, p. 906
• For labyrinthitis ossificans (late complication): serial CT and MRI to monitor for fibrous/bony obliteration of the labyrinth

Treatment Protocol

1. Viral / Idiopathic (Serous without identified bacterial source)

• Prochlorperazine 12.5 mg IM or 5-10 mg PO/PR
• Promethazine 25 mg IM/PO
• Dimenhydrinate 50 mg PO
• Betahistine (for longer-term labyrinthine compensation support)

• Ondansetron 4-8 mg IV/IM
• Metoclopramide 10 mg IV/IM

• Prednisolone 1 mg/kg/day tapering over 7-14 days - evidence for benefit in vestibular neuritis/viral labyrinthitis is moderate but supported in many guidelines; improves hearing recovery outcomes particularly in cases with SNHL. Cochlear NF-κB suppression before/with treatment is the proposed mechanism - Scott-Brown's, p. 924-925

• Not routinely recommended. Aciclovir or valaciclovir can be considered in Ramsay Hunt syndrome (VZV) or suspected HSV reactivation

• Early mobilization and balance exercises after the acute phase (days 3-5 onward)
• Supervised vestibular rehabilitation therapy (VRT) to accelerate central compensation

2. Serous Labyrinthitis (complicating AOM)

• Oral antibiotics targeting AOM pathogens (S. pneumoniae, H. influenzae, M. catarrhalis): amoxicillin-clavulanate (first-line), or amoxicillin 80-90 mg/kg/day in children
• Adjuvant corticosteroids (oral ± intratympanic) - data are lacking but may improve hearing outcomes - K.J. Lee, p. 922
• Myringotomy if middle ear infection unresolved with antibiotics
• Vestibular suppressants / antiemetics as above
• Symptoms are typically reversible with appropriate antibiotic treatment

3. Suppurative (Otogenic / Meningitic) Labyrinthitis - URGENT

• Parenteral antibiotics with CSF penetration - e.g., ceftriaxone 2g IV BD (covers S. pneumoniae, gram-negatives)
• Add metronidazole if cholesteatoma/anaerobic source suspected
• Duration: typically 4-6 weeks for severe otogenic infection

• Dexamethasone IV - shown to improve hearing outcomes in meningitic labyrinthitis due to H. influenzae and S. pneumoniae - K.J. Lee, p. 1004
• May prevent labyrinthitis ossificans if given in the initial phase - Scott-Brown's, p. 3923-3925

• Meningitis - LP if suspected, cover with appropriate antibiotics
• Labyrinthitis ossificans - serial CT/MRI if SNHL present
• Cochlear implantation (CI): early intervention if bilateral SNHL with signs of ossification developing. Once ossification progresses, the scala tympani is obliterated and CI becomes technically very difficult - K.J. Lee, p. 1008

4. Specific Etiologies

Complications

• Labyrinthitis ossificans - fibrous then bony obliteration of the membranous labyrinth; most common after suppurative labyrinthitis, especially meningitic. Cochlear T2 signal lost on MRI. May lead to profound bilateral deafness if cochlear implantation delayed
• Meningitis - bidirectional: labyrinthitis can cause or result from meningitis; risk elevated with cochlear implants, perilymph fistula, and congenital inner ear malformations
• Permanent profound SNHL - 2-20% (average ~10%) following bacterial labyrinthitis
• Persistent vestibulopathy - chronic dysequilibrium lasting months; requires VRT
• Brain abscess / intracranial extension - particularly from cholesteatoma-associated suppurative labyrinthitis

Key Diagnostic Distinctions

• Rosen's Emergency Medicine, p. 3628; Scott-Brown's Vol. 2, Table 62.4

• Shambaugh Surgery of the Ear (6e), pp. 3938-3948
• Cummings Otolaryngology Head & Neck Surgery, pp. 1835-1843
• Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol. 2, pp. 3888-3925
• K.J. Lee's Essential Otolaryngology (12e), pp. 867-1008
• Rosen's Emergency Medicine, p. 3628
• Textbook of Family Medicine 9e, pp. 537-539